Bioeconomic Factors of Beef Heifer Maturity to Consider when Establishing Criteria to Optimally Select and/or Retain Herd Replacements

Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building abioeconomic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy. The MI account for heifer age, birth BW, prebreeding BW, nutrition level, and dam size and age and is found to be inversely related to dystocia occurrence. On average there is a 2.2% increase in the probability of dystocia with every 1 point drop in the MI between the MI scores of 50 and 70. Statistically, MI does not directly alter second pregnancy rate; however, dystocia does. The presence of dystocia reduced second pregnancy rates by 10.67%. Using the probability of dystocia predicted from the MI in the sample, it is found that on average, every 1 point increase in MI added 0.62% to the probability of the occurrence of second pregnancy over the range represented by the data. Relationships among MI, dystocia, and second pregnancy are nonlinear and exhibit diminishing marginal effects. These relationships indicate optimal production and profitability occur at varying maturities, which are altered by animal type, economic environment, production system, and management regime. With these captured relationships, any single group of heifers may be ranked by profitability given their physical characteristics and the applicable production, management, and economic conditions

South Dakota Retained Ownership Demonstration

Three hundred seventy-four calves representing 44 cow-calf producers were consigned to a custom feedlot. Steer calves (254 head) consigned in October weighed 522 Ib initially, gained 2.91 1b per head daily, and averaged 1,100 Ib at slaughter after an average of 200 days on feed. Average cost of gain and profitability were $48.94 per cwt and -$12.03 per head, respectively. Steers consigned in January weighed 71 1 Ib initially, gained 3.07 Ib per head daily, and averaged 1,135 1b at slaughter after 141 days on feed. Average cost of gain and profitability were $43.59 per cwt and -$64.22 per head, respectively. Losses observed for 1994-95 were due to low carcass beef prices relative to the price of feeder cattle in fall of 1994 and January of 1995. As in previous years, average daily gain, days on feed, and quality grade appear related to differences in profit between cattle

South Dakota Retained Ownership Demonstration

Seven hundred six calves representing 81 cow-calf producers were consigned to a custom feedlot. Steer calves (421 head) consigned in October weighed 562 Ib initially, gained 2.75 Ib per head daily, and averaged 1153 1b at slaughter after an average of 207 days on feed. Average cost of gain and profitability were $61.48 per cwt and -$86.61 per head, respectively. Steers consigned in January weighed 738 Ib initially, gained 3.36 Ib per head daily, and averaged 1,196 Ib at slaughter after 137 days on feed. Average cost of gain and profitability were $55.55 per cwt and 4123.1 1 per head, respectively. Heifers consigned in January weighed 683 Ib initially, gained 3.17 Ib per head daily, and averaged 1063 1b at slaughter after 122 days on feed. Average cost of gain and profitability were$58.39 per cwt and -$95.63 per head, respectively. Severe losses observed for 1993-94 were due to a crash in the carcass beef market in late May through July as compared to the previous 3years of the Retained Ownership Demonstration. As in previous years, average daily gain, days on feed and percentage of choice appear to be related to differences in profit between cattle

Distribution of Major Health Risks: Findings from the Global Burden of Disease Study

BACKGROUND: Most analyses of risks to health focus on the total burden of their aggregate effects. The distribution of risk-factor-attributable disease burden, for example by age or exposure level, can inform the selection and targeting of specific interventions and programs, and increase cost-effectiveness. METHODS AND FINDINGS: For 26 selected risk factors, expert working groups conducted comprehensive reviews of data on risk-factor exposure and hazard for 14 epidemiological subregions of the world, by age and sex. Age-sex-subregion-population attributable fractions were estimated and applied to the mortality and burden of disease estimates from the World Health Organization Global Burden of Disease database. Where possible, exposure levels were assessed as continuous measures, or as multiple categories. The proportion of risk-factor-attributable burden in different population subgroups, defined by age, sex, and exposure level, was estimated. For major cardiovascular risk factors (blood pressure, cholesterol, tobacco use, fruit and vegetable intake, body mass index, and physical inactivity) 43%–61% of attributable disease burden occurred between the ages of 15 and 59 y, and 87% of alcohol-attributable burden occurred in this age group. Most of the disease burden for continuous risks occurred in those with only moderately raised levels, not among those with levels above commonly used cut-points, such as those with hypertension or obesity. Of all disease burden attributable to being underweight during childhood, 55% occurred among children 1–3 standard deviations below the reference population median, and the remainder occurred among severely malnourished children, who were three or more standard deviations below median. CONCLUSIONS: Many major global risks are widely spread in a population, rather than restricted to a minority. Population-based strategies that seek to shift the whole distribution of risk factors often have the potential to produce substantial reductions in disease burden

PEG−peptide conjugates

The remarkable diversity of the self-assembly behavior of PEG−peptides is reviewed, including self-assemblies formed by PEG−peptides with β-sheet and α-helical (coiled-coil) peptide sequences. The modes of self-assembly in solution and in the solid state are discussed. Additionally, applications in bionanotechnology and synthetic materials science are summarized

Adsorption of molecular brushes with polyelectrolyte backbones onto oppositely charged surfaces: A self-consistent field theory

The two-gradient version of the Scheutjens¿Fleer self-consistent field (SF-SCF) theory is employed to model the interaction between a molecular bottle brush with a polyelectrolyte backbone and neutral hydrophilic side chains and an oppositely charged surface. Our system mimics graft-copolymers with a cationic main chain (among which poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) or poly(l-lysine)-graft-polyoxazoline are well-known examples) interacting with negatively charged (metal oxide) solid surfaces. We aim to analyze the copolymer¿surface interaction patterns as a function of the molecular architecture parameters. Two regimes are investigated: First, we compute the effective interaction potential versus the distance from the surface for individual bottle brush macromolecules. Here, depending on the grafting ratio and the degree of polymerization of the side chains, the interplay of electrostatic attractions of the main chain to the surface and the steric repulsion of the grafts results in different patterns in the interaction potential and, therefore, in qualitatively different adsorption behavior. In particular, we demonstrate that, at high side chain grafting density and short grafts, the molecular brushes are strongly adsorbed electrostatically onto negatively charged substrates, whereas, in the opposite case of low grafting ratio and high molecular weight of grafts, the steric repulsion of the side chains from the surface dominates the polymer¿surface interaction. At intermediate grafting ratios, the adsorption/depletion scenario depends essentially on the ratio between the electrostatic screening length and the thickness of the molecular bottle brush. We further have analyzed the equilibrium adsorbed amount as a function of the macromolecular architecture. Our results are based on a detailed account of attractive and repulsive (including intermolecular in-plane) interactions, and suggest a nonmonotonic dependence of the adsorbed amount on the grafting ratio, in good agreement with the experimental studies for PLL-g-PEG adsorption onto Nb2O5 surfaces. The results of the theoretical modeling are discussed in the context of the optimization of the PLL-g-PEG molecular design parameters in order to create protein-resistant surfaces

Bending rigidity and induced persistence length of molecular bottle brushes : a self-consistent-field theory

The two-gradient version of the Scheutjens-Fleer self-consistent-field (SF-SCF) approach is employed for the analysis of the average conformations of side chains and corresponding contribution to the bending rigidity, or equivalently the induced persistence length, of molecular bottle brushes both under good and theta solvent conditions. This study is targeted to unravel conformational properties of poly(L-lysine)-graft-poly(ethylene glycol) copolymers in dilute aqueous solutions, where variation of temperature changes the solvent strength for poly(ethylene glycol) in a wide range. We focus on molecular brushes with moderate and high grafting density and large degree of polymerization of grafted chains. In this limit the predictions of an analytical mean-field theory for the dependences of the structural properties of the bottle brush on the architectural parameters are well confirmed. Both the induced persistence length and the ratio between the induced persistence length and the cross-sectional thickness of the bottle brush increase with increasing grafting density and/or increasing degree of polymerization of the grafted chains. However, in the range of moderate chain lengths and grafting densities this ratio remains small, which explains why the effects of the induced bending rigidity on the apparent persistence length have not been observed in earlier numerical experiments. We argue that only molecular bottle brushes with densely grafted long chains possess the potential for lyotropic ordering, both in solutions and at interfaces, due to the expected high effective segment asymmetry

Stretch-Oriented Polyimide Films

Two thermoplastic polyimides one amorphous, the other crystallizable -- were subjected to isothermal stretching just above their glass transition temperatures. Room-temperature strengths in the stretch direction were greatly improved, and, moduli increased up to 3.6-fold. Optimum stretching conditions were determined. Introduction Polymer films are useful as transparent windows, as flexible structural elements, as electrical substrates, and as vapor barriers. Their optical, electrical, mechanical, and barrier properties can often be improved by in-plane film orientation brought about by stretching. Textile fibers, too, are highly dependent on drawing and annealing to optimize their strengths and stiffnesses. It is of interest, therefore, to explore the effects of drawing on thermoplastic aromatic polyimides, a class of thermally-stable, radiation-resistant polymers. Previous thermal deformation experiments 1,2 with various polyimides showed that some of them underwent straininduced cr..